Golf ball

ABSTRACT

A golf ball  2  includes a spherical core  4 , a cover  6  and a paint layer  8 . The core  4  includes a spherical center  10  and a mid layer  12 . The cover  6  is formed from a resin composition that includes a base resin and a fluorescent pigment. The paint layer  8  is formed from a resin composition that includes a base resin and a light-collecting fluorescent dye. A product of an amount of the light-collecting fluorescent dye per 100 parts by weight of the base resin in the paint layer  8  and a thickness (mm) of the paint layer  8  is higher than 5.0×10 −5  and lower than 2.0×10 −3 .

This application claims priority on Patent Application No. 2011-219859 filed in JAPAN on Oct. 4, 2011. The entire contents of this Japanese Patent Application are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to golf balls. Specifically, the present invention relates to colored golf balls.

2. Description of the Related Art

A golf ball includes a core and a cover. A general golf ball is colored in white. The coloring is achieved by dispersing titanium dioxide in the cover. The hiding power of titanium dioxide is high. The color of the core is hidden by titanium dioxide. The coloring may be achieved by dispersing a white pigment in a paint layer.

Most golf balls are white. Thus, a golf player may falsely recognize a ball of another player as an own ball. A golf player who has hit a ball of another player is penalized.

A mark is printed on a golf ball. The mark includes a brand name and a ball number. A golf player can distinguish an own ball from a ball of another player by a brand name. A golf player can distinguish an own ball from a ball of another player also by a ball number. A golf player approaches a ball and distinguishes the ball on the basis of a mark. Distinction based on a mark is difficult from a long distance.

There are golf balls that are colored in colors other than white. The golf balls are referred to as “color balls”. The color balls can easily be distinguished from white balls.

JP58-116370 discloses a golf ball in which a cover contains a coloring agent and a paint layer contains a coloring agent. The type of color of the coloring agent of the cover is the same as the type of color of the coloring agent of the paint layer. In the golf ball, even if the paint layer is partially damaged to expose the cover, the exposure is unnoticeable.

JP2007-160087 (US2007/0135234) discloses a golf ball having a cover containing a light-collecting dye. The golf ball has excellent visibility when being placed on lawn.

The appearance of the golf ball disclosed in JP58-116370 is inferior in transparency. The visibility of the golf ball is not sufficient. Even for the golf ball disclosed in JP2007-160087, there is room for improvement in visibility.

A light-collecting fluorescent dye has inferior compatibility with the base resin of a cover such as an ionomer resin or the like. From a resin composition for a cover which includes a light-collecting fluorescent dye, the light-collecting fluorescent dye bleeds. In the process for producing the golf ball disclosed in JP2007-160087, facilities, such as a mold, the screw of an extruder, a hose for transferring a resin composition, and the like, are stained with the light-collecting fluorescent dye. The production of the golf ball disclosed in JP2007-160087 is not realistic.

An object of the present invention is to provide a color golf ball having excellent distinguishability because of being colored and also having excellent visibility.

SUMMARY OF THE INVENTION

A golf ball according to the present invention comprises a core, a cover covering the core, and a paint layer covering the cover. The paint layer is formed from a resin composition that includes a base resin and a light-collecting fluorescent dye. A product of an amount of the light-collecting fluorescent dye per 100 parts by weight of the base resin in the paint layer and a thickness (mm) of the paint layer is higher than 4.0×10⁻⁵ and lower than 6.0×10⁻³.

In the golf ball according to the present invention, the paint layer includes the light-collecting fluorescent dye. Thus, the paint layer emits high-intensity fluorescence. In the golf ball in which the product of the amount of the light-collecting fluorescent dye and the thickness of the paint layer is higher than 4.0×10⁻⁵ and lower than 6.0×10⁻³, not only the color of the paint layer but also the color of the cover influence the appearance. The synergistic effect of the emitted color of the cover and the emitted color of the paint layer achieves excellent visibility of the golf ball.

Preferably, the paint layer includes 0.005 parts by weight or greater but 0.20 parts by weight or less of the light-collecting fluorescent dye per 100 parts by weight of the base resin. Preferably, the paint layer includes a perylene type dye and/or a naphthalimide type dye.

Preferably, the paint layer is transparent. Preferably, the paint layer includes no white inorganic pigment.

Preferably, the thickness of the paint layer is equal to or greater than 0.008 mm but equal to or less than 0.030 mm.

The cover can be formed from a resin composition that includes a base resin and a fluorescent pigment. Preferably, the resin composition of the cover includes 0.01 parts by weight or greater but 5.0 parts by weight or less of the fluorescent pigment per 100 parts by weight of the base resin. Preferably, the resin composition of the cover includes one or more fluorescent pigments selected from the group consisting of a xanthene type fluorescent pigment, an acridine type fluorescent pigment, a quinoline type fluorescent pigment, a thiazole type fluorescent pigment, and an aminoketone type fluorescent pigment.

Preferably, a type of color of the light-collecting fluorescent dye included in the paint layer is the same as a type of color of the fluorescent pigment included in the cover.

Preferably, the resin composition of the cover includes 0.05 parts by weight or greater but 5.0 parts by weight or less of a white inorganic pigment per 100 parts by weight of the base resin.

The core may be composed of a plurality of layers. Preferably, an outermost layer of the core is formed from a resin composition that includes 100 parts by weight of a base resin and 1.0 parts by weight or greater but 10.0 parts by weight or less of a white inorganic pigment.

Preferably, a color difference ΔE between a surface of the golf ball and a surface of a sphere consisting of the core and the cover is equal to or less than 20.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially cutaway cross-sectional view of a golf ball according to one embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following will describe in detail the present invention based on preferred embodiments with reference to the accompanying drawings.

A golf ball 2 shown in FIG. 1 includes a spherical core 4, a cover 6 positioned outside the core 4, and a paint layer 8 positioned outside the cover 6. The core 4 includes a spherical center 10 and a mid layer 12 positioned outside the center 10. The mid layer 12 is an outermost layer in the core 4. On the surface of the cover 6, a large number of dimples 14 are formed. Of the surface of the cover 6, a part other than the dimples 14 is a land 16.

The golf ball 2 preferably has a diameter of 40 mm or greater but 45 mm or less. From the standpoint of conformity to the rules established by the United States Golf Association (USGA), the diameter is particularly preferably equal to or greater than 42.67 mm. In light of suppression of air resistance, the diameter is more preferably equal to or less than 44 mm and particularly preferably equal to or less than 42.80 mm. The golf ball 2 preferably has a weight of 40 g or greater but 50 g or less. In light of attainment of great inertia, the weight is more preferably equal to or greater than 44 g and particularly preferably equal to or greater than 45.00 g. From the standpoint of conformity to the rules established by the USGA, the weight is particularly preferably equal to or less than 45.93 g.

The center 10 is formed by crosslinking a rubber composition. Examples of base rubbers for use in the rubber composition include polybutadienes, polyisoprenes, styrene-butadiene copolymers, ethylene-propylene-diene copolymers, and natural rubbers. Two or more rubbers may be used in combination. In light of resilience performance, polybutadienes are preferred, and high-cis polybutadienes are particularly preferred.

In order to crosslink the center 10, a co-crosslinking agent is suitably used. Examples of preferable co-crosslinking agents in light of resilience performance include zinc acrylate, magnesium acrylate, zinc methacrylate, and magnesium methacrylate. Preferably, the rubber composition includes an organic peroxide together with a co-crosslinking agent. Examples of preferable organic peroxides include dicumyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and di-t-butyl peroxide.

The rubber composition of the center 10 may include a coloring agent. When the mid layer 12, the cover 6, and the paint layer 8 are transparent, the color of the center 10 influences the color of the golf ball 2. Examples of coloring agents include dyes and pigments. When the center is colored in white, the rubber composition may include titanium dioxide.

According to need, various additives such as a filler, sulfur, a vulcanization accelerator, a sulfur compound, an anti-aging agent, a plasticizer, a dispersant, and the like are included in the rubber composition of the center 10 in an adequate amount. Synthetic resin powder or crosslinked rubber powder may also be included in the rubber composition.

The center 10 has a diameter of preferably 30.0 mm or greater and particularly preferably 38.0 mm or greater. The diameter of the center 10 is preferably equal to or less than 42.0 mm and particularly preferably equal to or less than 41.5 mm. The center 10 may be composed of two or more layers. The center 10 may have a rib on the surface thereof. The center 10 may be hollow.

The mid layer 12 is formed from a resin composition. A suitable polymer for the resin composition is an ionomer resin. Examples of preferable ionomer resins include binary copolymers formed with an α-olefin and an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms. Examples of other preferable ionomer resins include ternary copolymers formed with: an α-olefin; an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms; and an α,β-unsaturated carboxylate ester having 2 to 22 carbon atoms. For the binary copolymers and ternary copolymers, preferable α-olefins are ethylene and propylene, while preferable α,β-unsaturated carboxylic acids are acrylic acid and methacrylic acid. In the binary copolymers and ternary copolymers, some of the carboxyl groups are neutralized with metal ions. Examples of metal ions for use in neutralization include sodium ion, potassium ion, lithium ion, zinc ion, calcium ion, magnesium ion, aluminum ion, and neodymium ion.

For the mid layer 12, an ionomer resin and another resin may be used in combination. A particularly preferable resin that can be used in combination with an ionomer resin is a styrene block-containing thermoplastic elastomer. The styrene block-containing thermoplastic elastomer includes a polystyrene block as a hard segment and a soft segment. Examples of styrene block-containing thermoplastic elastomers include styrene-butadiene-styrene block copolymers (SBS), styrene-isoprene-styrene block copolymers (SIS), styrene-isoprene-butadiene-styrene block copolymers (SIBS), hydrogenated SBS, hydrogenated SIS, and hydrogenated SIBS. Examples of hydrogenated SBS include styrene-ethylene-butylene-styrene block copolymers (SEBS). Examples of hydrogenated SIS include styrene-ethylene-propylene-styrene block copolymers (SEPS). Examples of hydrogenated SIBS include styrene-ethylene-ethylene-propylene-styrene block copolymers (SEEPS). An alloy of an olefin and one or more members selected from the group consisting of SBS, SIS and SIBS and hydrogenated products thereof may be used in the resin composition of the mid layer 12.

Instead of an ionomer resin, other resins may be used for the mid layer 12. Examples of the other resins include polystyrenes, polyamides, polyesters, polyolefins, and polyurethanes. Two or more resins may be used in combination.

The resin composition of the mid layer 12 can include a white inorganic pigment. The core 4 that includes the mid layer 12 including the white inorganic pigment exhibits white color. The lightness of the golf ball 2 that includes the core 4 is high. The core 4 contributes to the visibility of the golf ball 2. In addition, the core 4 does not impair visibility provided by the emitted colors of the cover 6 and the paint layer 8. Examples of preferable white inorganic pigments include titanium dioxide, zinc oxide, barium sulfate, lithopone, white lead, and calcium carbonate. In particular, titanium dioxide is preferred.

In light of visibility, the amount of the white inorganic pigment per 100 parts by weight of the base resin is preferably equal to or greater than 1.0 parts by weight and particularly preferably equal to or greater than 4.0 parts by weight. In light of durability, resilience, and moldability of the golf ball 2, the amount is preferably equal to or less than 10.0 parts by weight.

The mid layer 12 has a thickness of preferably 0.2 mm or greater and particularly preferably 0.3 mm or greater. The thickness of the mid layer 12 is preferably equal to or less than 2.5 mm and particularly preferably equal to or less than 2.2 mm. The mid layer 12 has a specific gravity of preferably 0.90 or greater and particularly preferably 0.95 or greater. The specific gravity of the mid layer 12 is preferably equal to or less than 1.10 and particularly preferably equal to or less than 1.05.

The cover 6 is formed from a resin composition. The base polymer of the resin composition is an ionomer resin. The resin composition of the cover 6 can include the ionomer resin described above for the mid layer 12.

For the cover 6, an ionomer resin and another resin may be used in combination. Examples of a preferable resin that can be used in combination with an ionomer resin include binary copolymers formed with an olefin and an α,β-unsaturated carboxylic acid. Other examples of a preferable resin that can be used in combination with an ionomer resin include ternary copolymers formed with an olefin, an α,β-unsaturated carboxylic acid, and an α,β-unsaturated carboxylate ester.

Instead of an ionomer resin, other resins may be used for the cover 6. Examples of the other resins include polyurethanes, polystyrenes, polyamides, polyesters, and polyolefins. In light of spin performance and scuff resistance, polyurethanes are preferred. Two or more resins may be used in combination.

The resin composition of the cover 6 includes a fluorescent pigment. The pigment emits a fluorescent color. In the golf ball 2, the color of the cover 6 can be observed through the paint layer 8. The fluorescent pigment influences the color of the golf ball 2. The golf ball 2 has excellent visibility.

Examples of preferable fluorescent pigments include xanthene type fluorescent pigments, acridine type fluorescent pigments, quinoline type fluorescent pigments, thiazole type fluorescent pigments, and aminoketone type fluorescent pigments.

Specific examples of fluorescent pigments include trade names “EPO Color FP-3000 (Yellow)”, “EPO Color FR-40 (Orange)”, “EPO Color FP-20 (Red)”, and “EPO Color FP-10 (Pink)”, manufactured by UkSeung Chemical Co., Ltd.

The amount of the fluorescent pigment per 100 parts by weight of the base resin is preferably equal to or greater than 0.01 parts by weight but equal to or less than 5.0 parts by weight. The golf ball 2 in which the amount of the fluorescent pigment is equal to or greater than 0.01 parts by weight has excellent visibility. In this respect, the amount of the fluorescent pigment is more preferably equal to or greater than 0.1 parts by weight and particularly preferably equal to or greater than 1.0 parts by weight. The golf ball 2 in which the amount of the fluorescent pigment is equal to or less than 5.0 parts by weight has high lightness and thus has excellent visibility. The golf ball 2 in which the amount is equal to or less than 5.0 parts by weight also has excellent moldability and further can be obtained at low cost. In these respects, the amount of the fluorescent pigment is particularly preferably equal to or less than 4.0 parts by weight.

The resin composition of the cover 6 may include a white inorganic pigment. The resin composition of the cover 6 can include the white inorganic pigment described above for the mid layer 12. The lightness of the cover 6 including the fluorescent pigment and the white inorganic pigment is high. The cover 6 can contribute to the visibility of the golf ball 2. In light of visibility, the amount of the white inorganic pigment per 100 parts by weight of the base resin is preferably equal to or greater than 0.05 parts by weight and particularly preferably equal to or greater than 0.2 parts by weight. From the standpoint that the hiding property is not too great and thus photoluminescence sufficiently occurs by the fluorescent pigment, the amount of the white inorganic pigment is preferably equal to or less than 5.0 parts by weight and particularly preferably equal to or less than 0.5 parts by weight.

The paint layer 8 covers the cover 6. The paint layer 8 protects the cover 6. The paint layer 8 achieves excellent appearance of the golf ball 2. The paint layer 8 is formed by application of a paint. For the application, an electrostatic coating method, a spray gun method, a brushing method, a dipping method, or the like can be used.

The paint is composed of a resin composition. Examples of the base resin of the paint include polyurethanes, epoxy resins, polyesters, acrylic resins, and cellulose resins. In light of durability of the paint layer 8, two-component curing type polyurethanes are preferred.

A two-component curing type polyurethane is obtained by a reaction of a base material and a curing agent. A two-component curing type polyurethane obtained by a reaction of: a base material containing a polyol component; and a curing agent containing a polyisocyanate (including a polyisocyanate derivative), is preferred.

As the polyol component of the base material, a urethane polyol is preferably used. The urethane polyol has urethane bonds and two or more hydroxyl groups. Preferably, the urethane polyol has hydroxyl groups at its ends. The urethane polyol can be obtained by causing a reaction of a polyol and a polyisocyanate at such a ratio that the hydroxyl groups of the polyol component are excessive in mole ratio with respect to the isocyanate groups of the polyisocyanate.

The polyol used for producing the urethane polyol has a plurality of hydroxyl groups. Polyols having a weight average molecular weight of 50 or greater but 2000 or less and particularly 100 or greater but 1000 or less are preferred. Examples of low-molecular-weight polyols include diols and triols. Specific examples of diols include ethylene glycol, diethylene glycol, triethylene glycol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, and 1,6-hexanediol. Specific examples of triols include glycerin, trimethylol propane, and hexanetriol. Examples of high-molecular-weight polyols include polyether polyols such as polyoxyethylene glycol (PEG), polyoxypropylene glycol (PPG) and polyoxytetramethylene glycol (PTMG); condensed polyester polyols such as polyethylene adipate (PEA), polybutylene adipate (PBA) and polyhexamethylene adipate (PHMA); lactone polyester polyols such as poly-ε-caprolactone (PCL); polycarbonate polyols such as polyhexamethylene carbonate; and acrylic polyols. Two or more polyols may be used in combination.

The polyisocyanate used for producing the urethane polyol has a plurality of isocyanate groups. Specific examples of the polyisocyanate include aromatic polyisocyanates such as 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, a mixture (TDI) of 2,4-toluene diisocyanate and 2,6-toluene diisocyanate, 4,4′-diphenylmethane diisocyanate (MDI), 1,5-naphthylene diisocyanate (NDI), 3,3′-bitolylene-4,4′-diisocyanate (TODI), xylylene diisocyanate (XDI), tetramethylxylylene diisocyanate (TMXDI) and paraphenylene diisocyanate (PPDI); alicyclic polyisocyanates such as 4,4′-dicyclohexylmethane diisocyanate (H₁₂MDI), hydrogenated xylylene diisocyanate (H₆XDI) and isophorone diisocyanate (IPDI); and aliphatic polyisocyanates such as hexamethylene diisocyanate (HDI). Two or more of these polyisocyanates may be used in combination. In light of weather resistance, TMXDI, XDI, HDI, H₆XDI, IPDI, and H₁₂MDI are preferred.

In the reaction of the polyol and the polyisocyanate for producing the urethane polyol, a known catalyst can be used. A typical catalyst is dibutyl tin dilaurate. The proportion of the urethane bonds included in the urethane polyol is preferably equal to or greater than 0.1 mmol/g but equal to or less than 5 mmol/g. The urethane polyol in which the proportion is equal to or greater than 0.1 mmol/g can achieve desired scuff resistance of the paint layer 8. The urethane polyol in which the proportion is equal to or less than 5 mmol/g can achieve excellent followability of the paint layer 8 to the cover 6. In the paint layer 8 having excellent followability, a crack is unlikely to occur when the golf ball 2 is repeatedly hit. By adjusting the molecular weight of the polyol, which is the material for the urethane polyol, the proportion of the urethane bonds can be set in the above range. By adjusting the blending ratio of the polyol and the polyisocyanate as well, the proportion of the urethane bonds can be set in the above range.

From the standpoint that a time taken for the reaction of the base material and the curing agent is short, the weight average molecular weight of the urethane polyol is preferably equal to or greater than 4000 and more preferably equal to or greater than 4500. In light of adhesion of the paint layer 8 to the cover 6, the weight average molecular weight is preferably equal to or less than 10000 and more preferably equal to or less than 9000.

In light of adhesion of the paint layer 8 to the cover 6, the hydroxyl value (mg KOH/g) of the urethane polyol is preferably equal to or greater than 15 and more preferably equal to or greater than 73. From the standpoint that a time taken for the reaction of the base material and the curing agent is short and occurrence of a crack is suppressed, the hydroxyl value is preferably equal to or less than 130 and more preferably equal to or less than 120.

The base material may contain, together with a urethane polyol, a polyol that does not have any urethane bond. The aforementioned polyol that is the material for the urethane polyol can be used in the base material. Polyols compatible with the urethane polyol are preferred. From the standpoint that a time taken for the reaction of the base material and the curing agent is short, the proportion of the urethane polyol in the base material on the solid content basis is preferably equal to or greater than 50% by weight and more preferably equal to or greater than 80% by weight. Ideally, the proportion is 100% by weight.

The curing agent contains a polyisocyanate or a derivative thereof. The aforementioned polyisocyanate that is the material for the urethane polyol can be used in the curing agent.

The paint layer 8 includes a light-collecting fluorescent dye together with the base resin. The light-collecting fluorescent dye absorbs sunlight and emits fluorescence of a long wavelength. The golf ball 2 that includes the paint layer 8 including the light-collecting fluorescent dye has excellent visibility. The light-collecting fluorescent dye has excellent compatibility with the base resin of the paint layer 8. The light-collecting fluorescent dye particularly has excellent compatibility with polyurethanes. In the paint layer 8, bleeding of the light-collecting fluorescent dye is suppressed. The paint layer 8 has excellent weather resistance.

Examples of preferable light-collecting fluorescent dyes include perylene type dyes and naphthalimide type dyes. Specific examples of light-collecting fluorescent dyes include trade names “LUMOGEN F YELLOW 083”, “LUMOGEN F ORANGE 240”, “LUMOGEN F RED 305”, “LUMOGEN F PINK 285”, and “LUMOGEN F VIOLET 570”, manufactured by BASF Co., Ltd.

In the golf ball 2 according to the present embodiment, the resin composition of the paint layer 8 includes no white inorganic pigment. The paint layer 8 is transparent. In general, the thickness of the paint layer 8 is much smaller than the thicknesses of the mid layer 12 and the cover 6. Even when the paint layer 8 contains the light-collecting fluorescent dye, the color of the cover 6 is reflected in the color of the golf ball 2. The synergistic effect of the emitted color of the cover 6 and the emitted color of the paint layer 8 can achieve excellent visibility of the golf ball 2.

The product of the amount (parts by weight) of the light-collecting fluorescent dye per 100 parts by weight of the base resin and the thickness (mm) of the paint layer 8 is referred to as hiding index in the present specification. The hiding index is higher than 4.0×10⁻⁵ and lower than 6.0×10⁻³. In the golf ball 2 in which the hiding index is higher than 4.0×10⁻⁵, the color of the paint layer 8 contributes to visibility. In this respect, the hiding index is particularly preferably equal to or higher than 8.0×10⁻⁵. The paint layer 8 in which the hiding index is lower than 6.0×10⁻³ has excellent transparency. In the golf ball 2 in which the hiding index is lower than 6.0×10⁻³, the color of the cover 6 contributes to visibility. In this respect, the hiding index is particularly preferably equal to or lower than 1.0×10⁻³.

The amount of the light-collecting fluorescent dye per 100 parts by weight of the base resin in the paint layer 8 is preferably equal to or greater than 0.005 parts by weight but equal to or less than 0.20 parts by weight. In the golf ball 2 in which the amount is equal to or greater than 0.005 parts by weight, the color of the paint layer 8 contributes to visibility. In this respect, the amount is particularly preferably equal to or greater than 0.010 parts by weight. The paint layer 8 in which the amount is equal to or less than 0.20 parts by weight has excellent transparency. In the golf ball 2 in which the amount is equal to or less than 0.20 parts by weight, the color of the cover 6 contributes to visibility. In this respect, the amount is particularly preferably equal to or less than 0.15 parts by weight.

The paint layer 8 preferably has a thickness of 0.008 mm or greater but 0.030 mm or less. In the golf ball 2 in which the thickness is equal to or greater than 0.008 mm, the color of the paint layer 8 contributes to visibility. In this respect, the thickness is particularly preferably equal to or greater than 0.010 mm. In the golf ball 2 in which the thickness is equal to or less than 0.030 mm, the color of the cover 6 contributes to visibility. In this respect, the thickness is particularly preferably equal to or less than 0.020 mm.

The type of color of the fluorescent pigment of the cover 6 is preferably the same as the type of color of the light-collecting fluorescent dye of the paint layer 8. The synergistic effect of the fluorescent pigment and the light-collecting fluorescent dye which are the same in type of color achieves excellent visibility.

A color difference ΔE between the surface of the golf ball 2 and the surface of the sphere consisting of the core 4 and the cover 6 is preferably equal to or less than 20. In the golf ball 2 in which the color difference ΔE is in this range, the synergistic effect of the fluorescent pigment of the cover 6 and the light-collecting fluorescent dye of the paint layer 8 achieves excellent visibility. In this respect, the color difference ΔE is particularly preferably equal to or less than 10.

The color difference ΔE is calculated on the basis of the following mathematical formula.

ΔE=((ΔL*)²+(Δa*)²+(Δb*)₂)^(1/2)

In the mathematical formula, ΔL* is the difference between an index L* of the sphere and an index L* of the golf ball 2. In the mathematical formula, Δa* is the difference between an index a* of the sphere and an index a* of the golf ball 2. In the mathematical formula, Δb* is the difference between an index b* of the sphere and an index b* of the golf ball 2. L*, a*, and b* are indexes in the CIELAB color system. The indexes L*, a*, and b* are calculated by the following mathematical formulas.

L*=116(Y/Yn)^(1/3)−16

a*=500((X/Xn)^(1/3)−(Y/Yn)^(1/3))

b*=200((Y/Yn)^(1/3)−(Z/Zn)^(1/3))

In these mathematical formulas, X, Y, and Z are tristimulus values in an XYZ color system, and Xn, Yn, and Zn are tristimulus values of a perfect reflecting diffuser. The CIELAB color system is a standard specified by the International Commission on Illumination (CIE) in 1976. In Japan, the CIELAB color system is used in “JIS Z 8729”. L* is an index of lightness. a* and b* are indexes related to hue and saturation. For a*, a negative value indicates green, and a positive value indicates red. For b*, a negative value indicates blue, and a positive value indicates yellow. The measurement of the indexes is conducted by using the spectrophotometer “CM-3500d” manufactured by Konica Minolta Sensing, Inc. A light receiver is applied to the surface of the sphere or the golf ball 2 to conduct the measurement. As a light source, “a standard light D₆₅” is used. The color temperature of the light source is 6504 k. As a spectral sensitivity, “a view angle of 2°” is used. As a hole diameter, 8 mm is used.

In the golf ball 2, the light-collecting fluorescent dye is included in the paint layer 8 and no light-collecting fluorescent dye is included in the cover 6. Thus, staining of facilities in the process for producing the golf ball 2 is suppressed.

EXAMPLES Example 1

A rubber composition was obtained by kneading 100 parts by weight of a high-cis polybutadiene (trade name “BR-730”, manufactured by JSR Corporation), 27 parts by weight of zinc diacrylate, 0.5 parts by weight of diphenyl disulfide, 0.75 parts by weight of dicumyl peroxide, and an appropriate amount of zinc oxide. This rubber composition was placed into a mold including upper and lower mold halves each having a hemispherical cavity, and heated at 170° C. for 20 minutes to obtain a center with a diameter of 39.1 mm. The amount of zinc oxide was adjusted such that the weight of a golf ball is 45.5 g.

A resin composition was obtained by kneading 50 parts by weight of an ionomer resin (trade name “Himilan AM7329”, manufactured by Du Pont-MITSUI POLYCHEMICALS Co., Ltd.), 25 parts by weight of another ionomer resin (trade name “Himilan AM7337”, manufactured by Du Pont-MITSUI POLYCHEMICALS Co., Ltd.), 25 parts by weight of a styrene block-containing thermoplastic elastomer (trade name “Rabalon T3221C”, manufactured by Mitsubishi Chemical Corporation), and 10 parts by weight of titanium dioxide with a twin-screw kneading extruder. The center was covered with the resin composition by injection molding to form a mid layer with a thickness of 1.0 mm.

A resin composition was obtained by kneading 70 parts by weight of an ionomer resin (the aforementioned “Himilan AM7329”), 30 parts by weight of an ethylene-methacrylic acid copolymer (trade name “NUCREL N1050H”, manufactured by Du Pont-MITSUI POLYCHEMICALS Co., Ltd.), and 3 parts by weight of a fluorescent pigment (the aforementioned “EPO Color FP-3000 (Yellow)”) with a twin-screw kneading extruder. The mid layer was covered with the resin composition by injection molding to form a cover with a thickness of 0.8 mm.

A paint including a two-component curing type polyurethane as a base resin was prepared. A base material of the paint is a mixture of a polyether polyol and a polyester polyol. The hydroxyl value of the base material is 82 mg KOH/g. A curing agent of the paint is hexamethylene diisocyanate. The NCO:OH equivalence ratio of the paint is 1.2:1.0. The paint includes a light-collecting fluorescent dye (the aforementioned “LUMOGEN F YELLOW 083”). The amount of the light-collecting fluorescent dye is 0.02 parts by weight per 100 parts by weight of the base resin. The paint was applied to the surface of the cover with a spray gun. The paint was dried at a temperature of 40° C. for 120 minutes to obtain a paint layer with a thickness of 0.01 mm. In this manner, a golf ball of Example 1 having a diameter of 42.7 mm and a weight of about 45.5 g was obtained.

Examples 2 to 18 and Comparative Examples 1 to 5

Golf balls of Examples 2 to 18 and Comparative Examples 1 to 5 were obtained in the same manner as Example 1, except the specifications of the center, the mid layer, the cover, and the paint layer were as shown in Tables 6 to 10 below. The composition of the center is shown in detail in Table 1 below. The composition of the mid layer is shown in detail in Table 2 below. The composition of the cover is shown in detail in Table 3 below. The composition of the paint layer is shown in detail in Tables 4 and 5 below.

[Visibility]

A golf ball was placed on lawn. Ten golf players who were distant from the golf ball by 5 m evaluated visibility of the golf ball. The evaluation was categorized as follows on the basis of the number of golf players who determined that the golf ball was easily viewable.

A: 9 or more

B: 6 to 8

C: 4 to 5

D: 3 or less

The results are shown in Tables 6 to 10 below.

[Staining Property]

A case where staining of facilities with the light-collecting fluorescent dye did not occur in the process for producing a golf ball was rated as “A”, and a case where the staining occurred was rated as “B”. The results are shown in Tables 6 to 10 below.

TABLE 1 Composition of Center (1) (2) (3) BR730 100 100 100 Zinc diacrylate 27 27 27 Diphenyl disulfide 0.5 0.5 0.5 Dicumyl peroxide 0.75 0.75 0.75 Titanium dioxide 10 3 — Zinc oxide Appropriate Appropriate Appropriate amount amount amount

TABLE 2 Composition of Mid Layer M1 M2 M3 Himilan AM7329 50 50 50 Himilan AM7337 25 25 25 Rabalon T3221C 25 25 25 Titanium dioxide 10 3 —

TABLE 3 Composition of Cover C1 C2 C3 C4 C5 C6 C7 C8 C9 Himilan AM7329 70 70 70 70 70 70 70 70 70 NUCREL N1050H 30 30 30 30 30 30 30 30 30 Epo Color FP-3000  3 — — — 1 — — —  2 (Yellow) Epo Color FP-40 —  2 — — 1 — — — — (Orange) Epo Color FP-20 — —  2 — — — — — — (Red) Epo Color FP-10 — — —  2 — 1.5 — — — (Pink) LUMOGEN F — — — — — — — 0.05 — YELLOW 083 Titanium dioxide — — — — 0.2 0.5 — —  3

TABLE 4 Composition of Paint Layer P1 P2 P3 P4 P5 P6 Base resin 100 100 100 100 100 100 LUMOGEN F 0.02 0.05 0.1 — — — YELLOW 083 LUMOGEN F — — — 0.05 — — ORANGE 240 LUMOGEN F — — — — 0.05 — RED 305 LUMOGEN F — — — — — 0.05 PINK 285 LUMOGEN F — — — — — — VIOLET 570

TABLE 5 Composition of Paint Layer P7 P8 P9 P10 P11 P12 P13 Base resin 100 100 100 100 100 100 100 LUMOGEN F YELLOW — 0.02 — 0.005 0.2 0.007 0.15 083 LUMOGEN F ORANGE — 0.02 — — — — — 240 LUMOGEN F RED 305 — — — — — — — LUMOGEN F PINK — — — — — — — 285 LUMOGEN F VIOLET 0.05 — — — — — — 570

TABLE 6 Results of Evaluation Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Composition of core (3)   (3)   (3)   (3)   (3)   Composition of mid layer M1 M1 M1 M1 M1 Thickness (mm) of mid 1   1   1   1   1   layer Composition of cover C1 C1 C1 C2 C3 Thickness (mm) of cover 0.8  0.8  0.8  0.8  0.8  Composition of paint P1 P2 P3 P4 P5 layer Thickness (mm) of paint 0.01 0.01 0.01 0.01 0.01 layer Hiding index (10⁻⁴) 2.00 5.00 10.00  5.00 5.00 Visibility A A A A A Staining property A A A A A

TABLE 7 Results of Evaluation Ex. 6 Ex. 7 Ex. 8 Ex. 9 Ex. 10 Composition of core (3)   (3)   (3)   (3)   (3)   Composition of mid layer M1 M1 M1 M1 M2 Thickness (mm) of mid 1   1   1   1   1   layer Composition of cover C4 C5 C6 C7 C1 Thickness (mm) of cover 0.8  0.8  0.8  0.8  0.8  Composition of paint P6 P8 P6 P7 P2 layer Thickness (mm) of paint 0.01 0.01 0.01 0.01 0.01 layer Hiding index (10⁻⁴) 5.00 4.00 5.00 5.00 5.00 Visibility A A A B B Staining property A A A A A

TABLE 8 Results of Evaluation Ex. Ex. Ex. Ex. Ex. 11 12 13 14 15 Composition of core (1)   (2)   (3)   (3)   (3)   Composition of mid layer — — M1 M1 M1 Thickness (mm) of mid — — 1   1   1   layer Composition of cover C1 C1 C2 C2 C4 Thickness (mm) of cover 1.6  1.6  0.8  0.8  0.8  Composition of paint P2 P2 P2 P5 P7 layer Thickness (mm) of paint 0.01 0.01 0.01 0.01 0.01 layer Hiding index (10⁻⁴) 5.00 5.00 5.00 5.00 5.00 Visibility A B B B B Staining property A A A A A

TABLE 9 Results of Evaluation Ex. Ex. Ex. Ex. Ex. 16 17 18 19 20 Composition of core (3)   (3)   (3)   (3)   (3)   Composition of mid layer M3 — M1 M1 M1 Thickness (mm) of mid 1   — 1   1   1   layer Composition of cover C1 C1 C1 C1 C1 Thickness (mm) of cover 0.8  1.6  0.8  0.8  0.8  Composition of paint P2 P2 P5 P12 P13 layer Thickness (mm) of paint 0.01 0.01 0.01 0.01 0.01 layer Hiding index (10⁻⁴) 5.00 5.00 5.00 0.70 15.00  Visibility B B C B B Staining property A A A A A

TABLE 10 Results of Evaluation Com. Com. Com. Com. Com. Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Composition of core (3)   (3)   (3)   (3)   (3)   Composition of mid layer M1 M1 M1 M1 M1 Thickness (mm) of mid 1   1   1   1   1   layer Composition of cover C1 C8 C9 C1 C1 Thickness (mm) of cover 0.8  0.8  0.8  0.8  0.8  Composition of paint P9 P9 P9 P10 P11 layer Thickness (mm) of paint 0.01 0.01 0.01  0.008 0.03 layer Hiding index (10⁻⁴) 0.00 0.00 0.00 0.40 60.00  Visibility D B D D D Staining property A B A A A

As shown in Tables 6 to 10, the golf ball of each Example is evaluated highly. From the results of evaluation, advantages of the present invention are clear.

The golf ball according to the present invention can be used for playing golf on golf courses and practicing at practice ranges. The above descriptions are merely for illustrative examples, and various modifications can be made without departing from the principles of the present invention. 

What is claimed is:
 1. A golf ball comprising a core, a cover covering the core, and a paint layer covering the cover, wherein the paint layer is formed from a resin composition that includes a base resin and a light-collecting fluorescent dye, and a product of an amount of the light-collecting fluorescent dye per 100 parts by weight of the base resin in the paint layer and a thickness (mm) of the paint layer is higher than 4.0×10⁻⁵ and lower than 6.0×10⁻³.
 2. The golf ball according to claim 1, wherein the paint layer includes 0.005 parts by weight or greater but 0.20 parts by weight or less of the light-collecting fluorescent dye per 100 parts by weight of the base resin.
 3. The golf ball according to claim 1, wherein the paint layer includes a perylene type dye and/or a naphthalimide type dye.
 4. The golf ball according to claim 1, wherein the paint layer is transparent.
 5. The golf ball according to claim 4, wherein the paint layer includes no white inorganic pigment.
 6. The golf ball according to claim 1, wherein the thickness of the paint layer is equal to or greater than 0.008 mm but equal to or less than 0.030 mm.
 7. The golf ball according to claim 1, wherein the cover is formed from a resin composition that includes a base resin and a fluorescent pigment.
 8. The golf ball according to claim 7, wherein the resin composition of the cover includes 0.01 parts by weight or greater but 5.0 parts by weight or less of the fluorescent pigment per 100 parts by weight of the base resin.
 9. The golf ball according to claim 7, wherein the resin composition of the cover includes one or more fluorescent pigments selected from the group consisting of a xanthene type fluorescent pigment, an acridine type fluorescent pigment, a quinoline type fluorescent pigment, a thiazole type fluorescent pigment, and an aminoketone type fluorescent pigment.
 10. The golf ball according to claim 7, wherein a type of color of the light-collecting fluorescent dye included in the paint layer is the same as a type of color of the fluorescent pigment included in the cover.
 11. The golf ball according to claim 7, wherein the resin composition of the cover includes 0.05 parts by weight or greater but 5.0 parts by weight or less of a white inorganic pigment per 100 parts by weight of the base resin.
 12. The golf ball according to claim 1, wherein the core is composed of a plurality of layers, and an outermost layer of the core is formed from a resin composition that includes 100 parts by weight of a base resin and 1.0 parts by weight or greater but 10.0 parts by weight or less of a white inorganic pigment.
 13. The golf ball according to claim 1, wherein a color difference ΔE between a surface of the golf ball and a surface of a sphere consisting of the core and the cover is equal to or less than
 20. 